With a second five years of K02 support, the PI wishes to continue his career with an emphasis on research. His areas of interest focus on the neurobiological mechanisms underlying spatial cognition and related forms of learning. In addition to relief from normal teaching, the award will also provide the PI the opportunity to learn several new techniques related to the proposed studies and his future plans. Experiments are proposed which will attempt to elucidate how spatial information is processed in the mammalian brain, with emphasis on the role of head direction (HD) cells previously identified and described by the PI. It is the PI's goal to determine how sensory information is transformed into a Ahigh level cognitive signal@ representing space. In Aims 1 and 2, the PI will examine how the HD cell signal is generated. In Aims 3 and 4, the role of vestibular inputs on HD firing will be examined. Aim 5 will explore the role of GABAergic interneurons in defining the HD cells= firing patterns. Aim 6 examines the types of cues HD cells used to maintain a stable tuning curve when the animal enters a novel environment, while Aim 7 focuses on the link between the HD cell and space-directed behaviors. Lastly, Aim 8 examines how HD cells respond to planes other than Earth horizontal. The results of these experiments will have implications for understanding how the brain processes spatial information, and since spatial processing deficits are characteristic of age-related cognitive impairments, to understand the nature of these impairments in humans.